A closed-population mark-resighting estimate of the number of Spoon-billed Sandpipers at Leizhou Peninsula, Guangdong Province, China during the boreal winter

Abstract

Critically Endangered Spoon-billed Sandpipers Calidris pygmaea migrate from their breeding grounds in Russia to winter on the coasts of southern China and South-east Asia. Previous studies on Leizhou Peninsula, Guangdong Province, China have shown that the species is present there in winter, as well as during the autumn and spring migration periods. However, there have been no formal estimates of the number of birds present. In November–December 2020 we conducted systematic searches for Spoon-billed Sandpipers marked individually with leg flags at Tujiao (Leizhou Peninsula) and also made scan surveys there to estimate the proportion of birds with marks. We used these data in combination to make a closed-population mark-resighting estimate of the local population in the Tujiao study area of approximately 60 individuals. Our estimate and its lower 95% confidence limit are both considerably larger than the 33 birds found during a co-ordinated count at Donghai Island, Hebei and Tujiao combined a few weeks later. This may be because raw counts tend to miss some individuals and therefore underestimate the total. The total for Tujiao represents about 8% of the estimated world population in winter, making it the second most important known wintering site after the Upper Gulf of Mottama in Myanmar.